5-Fluorouracil (5-FU) is a pyrimidine analog which noncompetitively inhibits thymidylate synthase, interfering with DNA synthesis. It has been used for the treatment of cancer for several decades. Capecitabine is a fluoropyrimidine carbamate which acts as a prodrug, being enzymatically converted to 5-FU by enzymes concentrated in the liver and in cancer tissue. The selective localization of these processing enzymes, and in particular, thymidine phosphorylase in tumor tissues, targets the production of the active product, 5-FU, in cancer cells.
